Remove the border between the window title (bar) and content

Jul 20, 2012 at 11:51 AM

I have create a Window with Ribbons (2010 - Microsoft.Windows.Controls.Ribbon).

It looks like that:

enter image description here

Now, is there a border over the tabs (between the tabs and the title). This is very ugly.

It should looks like Microsoft Office Word:

enter image description here

What can I do, that there is no border between the tabs and the titlebar?

(The RibbonWindow is used)